Modern refrigerator appliances use a gas-based refrigerant to provide cooling for the fresh food and/or freezer compartment of the refrigerator. The refrigerant is circulated within a loop that includes passage through the inside compartment(s) of the refrigerator. Heat is withdrawn from inside the refrigerator by blowing air across an evaporator in which the refrigerant changes state from a liquid to a gas by absorbing heat energy from the air. The chilled air is circulated throughout the inside of the refrigerator to lower the temperature, including food items, in the internal compartments. Thereafter, the refrigerant is compressed and subsequently cooled by passage through a heat exchanger—more commonly referred to as a condenser. The condenser is typically exposed to ambient air for heat exchange therewith.
Due to the repeated passage of air over the evaporator, moisture in the air will eventually condense and become frost on the coils of the evaporator. As a fan blows more air across these coils, if left unchecked, a frost load will continue to build-up on the evaporator. This build-up is undesirable because e.g., it decreases the cooling efficiency of the evaporator and therefore increases the energy usage of the refrigerator. In addition, in order to maintain a constant flow of air through the internal compartments despite the resistance caused by the ice build up, increased power is required to maintain the fan at a constant target speed.
Accordingly, most refrigerator appliances make use of a defrost cycle in order to remove and reduce the build-up of ice on the evaporator. Several techniques can be used to effect the defrost cycle. For example, some refrigerators use a heater to melt the ice away from the evaporator. The defrost cycle may be triggered by temperature sensors located near the evaporator or otherwise in the freezer compartment. Some refrigerators may use timers that automatically defrost after some predetermined period of time. Still others may use complex algorithms that determine a defrost cycle based on variables such as e.g., how many times the refrigerator doors have been opened allowing moisture-laden air into the internal compartments.
Executing a defrost cycle causes the refrigerator to consume more energy. For example, the heaters for melting the ice require energy to operate. Depending upon the length of the defrost cycle, the refrigerator will consume additional energy cooling the internal compartments of the refrigerator back to the desired temperatures upon completion of the defrost cycle. Thus, unnecessary operation of the defrost cycle is undesirable.
Additionally, there may be times during which operation of the defrost cycle is more cost effective than at other times. Electric utilities are typically required to provide generation equipment capable of handling peak energy demand periods caused by similar use patterns among customers such as e.g., early morning usage as multiple customers awake and begin to consume electricity in starting and preparing for the day. This additional equipment comes at additional capital and operating expense, which must ultimately be borne by the consumer. Some utilities may even increase their charges per energy unit for usage during these periods of peak energy demand versus usage at non-peak times.
Accordingly, a refrigerator that can more accurately determine when to initiate a defrost cycle would be useful. A refrigerator that can also predict when a defrost cycle will be necessary and determine whether such defrost cycle should be delayed or accelerated based on peak electricity demand periods and/or periods of increased electricity cost would also be particularly beneficial.